If you have an email list of only 100 people, then any A/B testing is worthless because your sample size is too small. You could A/B test the exact same email and the results would say one is better than the other.

You need thousands of emails in order to get a usable analysis of the A/B test. If the sample size is too small, then you're only getting data on which 50 people are more engaged, not which email is actually more usable.

You could create an A/B test that the data shows one email is more effective, but it's actually less effective because some of the people on the other half don't check that email address anymore.

Except you cannot guarantee that the stand out in the list of 100 is a stand out because of the email or because your sample size is too small.

A/B testing on a 6mil list is worth it.

A/B testing on a small email list will most likely provide worthless data and there's much more useful things you can be spending your time on - like growing your list.

Let's look at the 100 number again. If you get a 20 Open out of 50 for one and 10 open out of the other 50, then you might say one performed twice as good as the other. But if the lower performing had an email list of 20 emails of people that rarely check their email and/or are email addresses specifically for signing up for the newsletter to get the benefit, then your data is wrong and the under performing email is actually the better email, but you don't know that.

The margin for error is simply way too high on small email lists to trust the results.

Well now you get into statistics. A smaller sample size requires a larger impact to be statistically relevant. Otherwise you could just be looking at random noise.

Think about it at it's simplest terms. You have a list of 2 people. You A/B test your subject line and one of them opened. Are you sure it was the subject line or could it just be random chance?

On the other extreme you have 10,000 people. You A/B test your subject line and all 5,000 people who got version A opened, while all 5,000 people who got version B did not. We can be confident that there is something wrong with B (probably ended up in spam).

For that 10,000 person list, if there was only a change of 1 open, we go right back to being random chance.

So now the tricky part is determining what size/impact is necessary to feel confident the change in engagement wasn't just random chance. This is much more difficult than most people expect and can't be explained on reddit, but here are some good resources:

It's not necessarily too small to do testing, but you have to be careful with how/what you test. Tests are best done on established designs/subject lines with smaller variations between them. Also, I generally suggest at least a few full 50/50 splits with smaller lists to make sure your numbers are not skewed. Take all testing with a grain of salt and don't hesitate to continually confirm your findings over time as your list grows.

Admittedly, I'm a little jaded on testing. I tested identical emails sent at identical times to 1m in each version. Opens were 35% for one version and 40% for the other. Clicks seemed to have a similar disparity as well. This was very much an outlier though. As long as you test over multiple campaigns, you should be good.

Email marketing is one of the best way to get reads, however you should know the end to end process, even if you loose even a single step the campaign will go wrong, check with email marketing experts to get the best result on email campaign.

Sometimes it’s hard to tell the difference between true digital marketing experts and just plain posers. The worst advice I’ve ever heard was to focus all efforts on one channel – social media. Don’t get me wrong; social media is an extremely valuable channel. But, the best results will come from taking a multi-channel approach to digital marketing by targeting customers across channels – email, mobile, social, SMS, etc.

Some might argue that email is less effective when compared to mobile, social and other mainstream channels. However, when done in the right way, the ROI achieved through email marketing can almost double ROI generated through other channels.

Anyways, if you want some good advice when it comes to email, here are some tips to consider: Key Factors of Successful Email Marketing